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https://ntrs.nasa.gov/search.jsp?R=19760009633 2020-07-28T13:46:19+00:00Z

NASA TECHNICAL NASA TM X -72817MEMORANDUM

000 (NASA-TM-X-72617) DESIGN, FABRICATION AND N76-1672

N SYSTEMS INTEGRATION OF A SATELLITE TRICKED,

~ FREE-DRIFTING OCEAN DATA BUOY (NASA) 24 pUnclas

HC $3.50CSCL 08C

G3/48 13569

f-

4Z

1

DESIGN, FABRICATION AND SYSTEMS INTEGRATION,

OF A SATELLITE TRACKED, FREE-DRIFTING OCEAN DATA BUOY

R

John W. Wallace and JohnW. Cox FEB 191;C'7 RECEIVED

NASA STI FAMWINPUT BRAIM

'^ ^r rr1 /1r^

This informal documentation medium is used to provide accelerated orspecial release of technical information to selected users. The contents

may not meet NASA formal editing and publication standards, may be re-vised, or may be incorporated in another publication.

NATIONAL AERONAUTICS AND SPACE ADMINISTRATION

LANGLEY RESEARCH CENTER, HAMPTON, VIRGINIA 23665

A'

1. ft"M No Z. Goverwoent Aoowion No. 3. Redpient'e Catalog No.-7NASA TM X-72817

4. Title and SuNtie

Design, Fabrication and Systems Integration

5 Rupert DewJanuary 1976

of a Satellite Tracked, Free-Drifting OceanData Buoy

T. haherm Pogo of* Or"nitation Reprt No.Wallace, John W.Cox, John W. 10 Work Unk No

644-02-02-01Y. Pleft nS0WAndon Nnaa and A"=

National Aeronautics and Space Administration tt. Conenct a ter►t No. Langley Research CenterHampton, Virginia 23665

13. Type of Report and Pwiod Cowed

Technical Memorandum12. sp nwriry Apnoy Wme end Addnn

National Aeronautics and Space Administration 1^. Spone A Wq Aprwy CodsWashington, D. C. 20546

It Supplanrntry Now

16. Abtraot I

This paper presents engineering details of a small free-drifting buoyconfiguration designed for use in the study of continental shelf watercirculation patterns in the Chesapeake Bight of the Western North Atlantic !Ocean. The buoy incorporated French instrumentation and was interrogated bythe French EOLE ( God of the Wind) satellite to provide position and fourchannels of temperature data. The buoy design included a variable depthdrogue ( sea anchor) and a power supply sufficient for 6 weeks of continuousoperations. Proof tests of the configuration indicated an adequate designand subsequent field experiments verified the proper functioning of thesystem.

i

17. Key Words (&jnwW by Authr(sl l iSTAR eatepry underlined) 10. Dietribution Statanetnt

Free Drifting Buoys, Ocean Data SystemsOceanography , Physical S^iences, Unclassified - Unlimited

!

ucean Buoy Tracking1

19. Security CJntif. tot" report) 20. Smaxity CIN1if. lot " pole) 21. No. of ftm 22. Prim*

Unclassified I Unclassified 23 3.75

DESIGN, FABRICATION AND SYSTEMS INTEGRATION

OF A SATELLITE TRACKED, FREE-DRIFTING OCEAN DATA BUOY

by

John W. Wallace and John W. Cox

SUMMARY

Engineering details and development tests are presented for a small(~250kg) free-drifting buoy system used in water circulation studies on thecontinental shelf of the United States East Coast. The buoy was designedspecifically to incorporate a standard size rack unit of instrumentationobtai:,ed from the French Centre National D'Etudes Spatiales (CNES) through theCAS-A office at the National Aeronautics and Space Administration's (NASA)Goddard Space Flight Center (GSFC). Data transmitted from the buoy to theFrench EOLE satellite included four channels of temperature data and the buoyidentification. Buoy position was determined by satellite measurement ofrange and range-rate plus the satellite orbital parameters determined fromground tracking station data.

High priority was given, during design, to factors influencing ease of• deployment and retrieval from ships and helicopters and to planned refurbish-

ment. The resulting system proved to be suitable for.the planned missionsand were capable of operation for approximately 6 weeks. Although thesemissions were usually 2 weeks long, on one occasion the system survived adrift of more than 16 months in crossing the Atlantic Ocean from Virginia toSpain.

INTRODUCTION

One of the major goals of NASA for the 1970's is the application of spacetechnology and capabilities to societal needs and environmental problems.Langley Research Center (LaRC), as part of the program, has been working withstate and other federal agencies in studying the use of satellites and free-drifting buoy systems for remote measurement of current, temperature, salinity,sea state, and other ocean and air-sea interface parameters.

The measurement, of ocean circulation with free-drifting buoys has previouslybeen limited by the high costs of ships tracking the buoys. With the recentavailability of satellite tracking systems, the use of free-drifting buoy .measurements to obtain circulation features has become more economical. TheEOLE (God of the Wind) buoy system used in this investigation included asurface float (buoy) and large crossed plates suspended by a chain to couplethe buoy to the water at the depth of interest. This configuration is anacceptable "current drogue" to most of the oceanographic community.

41

The buoy system wasand transponder system tcChesapeake Bight. This aBay to Cape Hatteras, hasdefense, and recreation,sources.

designed to use the existing French BOLE satellitemeasure water circulation and temperature in the

rea of the Atlantic Ocean, extending from Delawarean important role in commerce, fishing, national

and is a focal point in the search for new oil

Data transmitted from the buoy to the BOLE satellite included fourchannels of temperature data and the buoy identification. Buoy position wasdetermined by satellite measurement of range and range rate, plus thesatellite orbital parameters determined from ground tracking station data.Data from three of the deployments are reported in references 1 and 2. Althoughthese missions were usually 2-week drifts, on one occasion the buoy surviveda drift of more than 16 months in crossing the Atlantic Ocean from Virginiato Spain.

This report presents engineering details for the BOLE buoy system. Alsodescribed are analytical results and experimental tests designed to insureproper and reliable operation of the system.

BUOY DESCRIPTION

The BOLE buoy system was composed of two units; a surface float-instrumenthousing (buoy) and a weighted cross-type drogue. The two units were linkedby a 0.635 cm galvanized chain of variable length. The total mass of thesystem was 245 kg. The instrument housing contained the buoy instrumentationand power supplies. The drogue served to couple the instrument housing to themovements of subsurface currents. The chain length could be varied to allowcoupling to currents from 5 to 30 meters below the surface. Table 1 is a listof buoy components with the engineering drawing number for each component.Figure 1 shows the major external dimensions of the buoy and drogue. Figure 2shows an assembled BOLE buoy ready for deployment.

The instrument housing was divided into two compartments with the uppercompartment containing the BOLE transponder and the lower compartmentcontaining the power supply and other instrumentation. A flotation diskdesigned to maintain a low wind profile was atop the instrument housing. Thedisk was painted with fluorescent paint as a location aid for visual trackingand recovery. A small incandescent light was mounted on the flotation diskfor navigational safety and ease in locating the buoy at night. The lightflashed once every 3 seconds. A hoisting assembly and an BOLE antennawith housing were attached to the buoy through the flotation disk. Figure3 shows the surface float-instrument housing with the major components labeled.

The drogue was four aluminum plates, with stiffeners, fastened to forma cross. Self-contained data recorders could be attached to the drogue toprovide additional data. Lead ballast was attached to the drogue where less

2

Four temperature sensors were attached to the chain linking the instrumenthousing and drogue. Location of the sensors was variable.

Structural Design

The SOLE buoy structure was designed to incorporate inexpensive materialsand fabrication methods in a structure that would withstand harsh environmentalconditions. The buoy was designed to operate in a temperature range of -20Cto 350C, and to withstand 20 -25 foot seas (sea state 7) and handling loadsof 1 to 2 g's. Relevant structural components and dimensions of the buoyare pointed out in figure 1.

Two methods were used to fabricate the instrument housing. The initialhousings, shown in figure 5(a), were made of fiberglass blown onto a woodenmold. In use, the fiberglass housings could not withstand the pounding ofthe sea and the fiberglass cracked. This resulted in a change to stronger butless expensive housings. The later housings, shown in figure 5(b), wereconstructed from welded and machined aluminum plates. The housing was arectangular box with one side open to allow placement and removal of theinstrumentation. Interior dimensions of the housing were 0.584 m long,0.490 m wide, and 0.452 m high. A 0.953 cm thick aluminum cover plate and0.318 cm nominal diameter 0-ring were used to seal the housing. The coverplate is shown in figure 6.

The flotation disk atop the instrument housing was a 91.440 cm diametercylindrical body with a conical top. The cylinder was 6.350 em high and thecone was 3.810 cm for a total height of 10.160 cm. The material was a 0.254 cmthick fiberglass shell bonded to a load-carrying structure of wood andphenolic material. The disk was filled with closed cell expandable foam.Four phenolic posts, protruding through the disk, supported the EOLE antennaassembly. Figure 7 is a photograph of the flotation disk opened to show theinner structure.

The hoisting assembly cradled the instrument housing and passed throughthe flotation disk. The lifting bail, used to deploy and retrieve the buoy,was attached to the top of the hoisting assembly. The lower part of thehoisting assembly was a standard 7.62 cm steel channel to which the droguechain was attached. In figure 8, a photograph of the bottom of the instrumenthousing, the steel channel is shown with the chain attached. The chain was0.635 cm proof coil galvanized steel with a working strength of 5560 newtons.A swivel was used to attach the chain to the drogue so that rotational motionof the drogue was not transmitted to the surface unit.

a

The drogue was constructed of 0.318 cm thick aluminum plates fastened in

v the form of a cross and braced with 2.54 cm aluminum angles. The maximumwidth and height of the drogue was 152.4 cm. Figure 9 snows the assembleddrogue with the swivel and braces.

r,77T7---1

Instrumentation

Instrumentation on the EOLE buoy included an EOLE transponder and antenna,ur temperature sensors, recovery beacons, and power supplies.

The transponder (shown in figure 10) was, located in the upper compartmentthe instrument housing and communicated with the EOLE satellite, trans

-tting buoy identification, calibration, and temperature data. Thetransponder had a length, width, and height, respectively, of 50.4 cm, 48.3 cm,and 22.1 cm. The transponder mass was 25 kg. The antenna (figure 11) wasa sunk plane, cavity backed spiral type 36.0 em in diameter and 26.0 cm high.The antenna mass was 5.58 kg.

Each temperature sensor was a standard therm stir ::ith negativetemperature coefficient, soldered to the end of an oceanographic cable. Thethermistor and connection were encased in epoxy and a protective film ofneoprene rubber. The cable connecting the sensor to the transponder was a2-conductor, 18-gage wire with a neoprene covering. Each cable was securedto the chain independently for ease of replacement.

Figure 12 shows two temperature sensors attached to the chain. The smallsensor on the left is the normal, uninsulated sensor and has a quick responseto temperature changes. The large sensor has a thick layer of foam insulationto delay its response so it indicates onlr r long-term temperature changes.

The buoy contained two radio transmitters (called recovery beacons) whichbroadcast on a frequency of 235 Mhz. The first beacon operated continuously whilethe second operated only on command from the satellite or if there wa:3 a powerfailure to the transponder. Operation of the second beacon was regulated bya solar switch, allowing daylight only operation to conserve battery power.The recovery beacon antennas were wire whip antennas (quarter-wave) solderedto a wire mesh ground plane embedded in the top of the flotation disk. Theantennas were coated with silicone rubber for protection from the environment.The beacon antennas are visible in figure 3.

The lower compartment of the instrument housing contained an instrumentdeck, shown in figure 13, on which were mounted the remaining instrumentationand the power supplies. All power for the buoy system was provided by 1.5-voltdry-cell batteries, divided into four packs. Packs 1, 2, and 3 each contained12 batteries and provided power, respectively, for the transponder, thecontinuous recovery beacon, and the daylight only beacon. Pack 4, with 5batteries, powered two programers mounted on the deck. A checkout plug andtwo on-off plugs mounted near the front of the deck were accessible through asmall port in the instrument housing cover plate. Figure 10 shows the instrumenthousing with all instrumentation in place.

k

f

Physical Properties

Presented in table 2 is a list of buoy components and some of the physicalproperties of the components used for b-#:oyancy calculations. The dry mass andgravity force are the total mass and force for the component. The buoyantforce is calculated for those parts of the system below the water line. TheEOLE antenna was completely above water, therefore, it did not contribute tothe buoyancy of the system. The flotation disk was partially submerged,therefore, the buoyant force represented only th-t portion below water. Allother components (including batteries, instrument deck, and EOLE transponder)were within the instrument housing and were completely submerged. Theinstrument housing buoyant force was calculated on the volume of the housingexcluding the cover plate which was calculated separately.

Measured values for mass, center of gravity (c.g.), and moments ofinertia, Ixx, Iyy, and Izz for the X, Y, and Z axes, respectively, are presentedin figure lb for an aluminum buoy. Figure 15 presents the same values for afiberglass buoy. By comparing the figures, it can be seen that the changein material produced very little change in the properties. The mass, c.g., andmoments of inertia for the drag plates are presented in figure 16. A11 inertiameasurements were taken in air by both the compound pendulum and bifilar methods.The measurements from both methods were in close agreement.

TEST PROGRAM

A series of tests were performed on the components of the EOLE buoy toinsure the proper operation of the system. Descriptions of the tests arelisted below.

Solar Cell Panel.- To determine any adverse effects of salt depositson the operation of a solar cell panel, a mockup of the panel area, shownin figure 17, was built and ballasted to give proper flotation depth. The mockupwas placed between posts in salt water and tied with enough slack in the linesto allow free movement with the tide and wave action. After 2 weeks themockup was removed from the water and the solar cell electrical output wasmeasured. The test showed there was not enough material deposited on thepanel to significantly affect the solar cell operation.

Thermal Analysis.- The instrument housing was analyzed to determine itsadequacy for maintaining temperature limits for the instrumentation. A freeconvection approach was used in the analysis (ref. 3). Instrument heatdissipations in the standby and transmission modes and varying water temperatureswere considered in the calculations. The analysis showed the structural design,using either fiberglass or aluminum, would maintain the proper temperature limitsinside the instrument housing in water having a temperature range greaterthan the range expected in the ocean study area.

5

Antennas.- Antenna tests were conducted in the LaRC Anechoic Chamberto determine optimum locations for the recovery beacon antennas. The mosteffective positions were 900 apart on a radius of 26.67 cm from the centerof the BALE antenna. Figure 18 shows the antennas set up in the AnechoicChamber. The tests also showed distortion of the beacon antenna pattern fromtwo causes. One, the lifting bail caused distortion when in a recliningposition on the same side of the buoy as the beacon antennas. This wasalleviated by installing retainers on the bail to confine movement to theopposite side of the buoy. The other cause, bolts holding the ROLE antennaassembly, was corrected by insulating the bolts from the BOLE antenna mountingring.

Flotation Test.- One constraint in the design of the buoy was a lowwind profile. The waterline for minimum freeboard of the buoy was located2.54 cm above the bottom surface of the flotation disk. The buoy, originallydesigned for prnper flotation with 10 meters of chain, needed additional buoyancywhen the chain length was increased to 30 meters. To determine needed buoyancy,a buoy with no flotation aids and with weights attached to simulate the drogueand 30 meters of chr_n was placed in sea water. Blocks of foam were attachedto the buoy until it floated at the predetermined water line. Durableflotation blocks were then designed and permanently attached to the buoy.With the flotation blocks, the buoy system maintained 222.42 newtons positivebuoyance. Figure 19 shows the buoy rigged for the flotation test.

Warning Light.- A life expectancy test on a continuously-runningprototype of the self-contained warning light showed the light could maintaina sufficient light level for 8 weeks. A warning light can be seen mountedon the buoy in figure 3. Figure 20 shows the components needed to constructa warning light and a completed light.

Ground Simulation.- BOLE satellite functions were simulated on the groundby use of a system of packaged units provided by Centre National d'EtudesSpatiales (CNES). The simulation system interrogated the BOLE transponderand relayed coded signals to the transponder to activate buoy subsystems.It also displayed oscillator frequencies which represented the sensorreadings. The buoy could either be hard wired to the simulation systemfor interrogation, or it could be interrogated through the BOLE antenna. Thesimulation system was used to verify proper operation of all buoy systems beforethe buoy was deployed.

Prototype gift Test.- As a field test of the structural and instrumentationsystems, a working prototype of the first EOLE buoy was deployed in the AtlanticOcean on September 26, 1972. While the buoy drifted free for 2 days, thebuoy fluid dynamics were visually observed in situ. These observationsdisclosed that in calm seas the buoy had a freeboard of approximately 3 cm,while in high seas of 1.3 m or more, the buoy was completely submerged onseveral occasions. There was no indication of rotation of the surface unitor of any unstable pendulum motion. Figure 21 shows the buoy in the waterduring the test.

6

.....

After recovery, an inspection of the buoy showed that all instrumentcomponents and all exterior structural fittings were still solidly mounted.There was no moisture inside the instrument housing. Buoy positionsrecorded onboard the vessel which deployed the buoy and positions fromsatellite data compered favorably. Buoy sensor temperature data relayed bysatellite were comparable to data from a thermograph attached to the buoy.The drift test indicated that the BOLE buoy structural and instrumentationdesigns were adequate for the planned studies of the United States EastCoast continental shelf waters.

CONCLUDING REMARKS

The free-drifting EOLE buoy system was designed to utilize the FrenchEOLE satellite and transponder system to study water circulation patternsand temperatures on the continental shelf of the United States East Coast.The buoy system, designed and fabricated at Langley Research Center, hasbeen constructed with both aluminum and fiberglass instrument housings(the fiberglass housing was found to be structurally inadequate). The BOLEsatellite and transponder and other instrumentation provided buoy positionand four channels of temperature data. An onboard power supply allows allsystems to operate continuously for 6 weeks.

A drogue is attached to the buoy by a chain that can be varied in lengthfrom 5 raters to 30 meters. The drogue allows the buoy to be coupled withsubsurface currents. Thermistors may be attached to the chain to obtainwater temperatures to a depth of 30 meters. Recovery beacons are provided toaid in locating the buoy for visual tracking or recovery. All components,as well as the complete buoy system were tested to ensure satisfactoryoperation and structural integrity.

On deployments to date EOLE buoy systems have been through coastalstorms, they have been washed up on beaches, and one buoy survived a 16-month drift across the Atlantic Ocean to Spain. Experience shows that theBOLE buoy system is capable of operating in and withstanding severeenvironmental conditions.

References

1. Usry, J. W.; and Wallace, John W.: Data Report of Six Free-DriftingBuoys Tracked by the IOLE Satellite in the Western North AtlanticOcean in the Autumn of 19T2. NASA TMX-T2645. Undated.

2. Wallace, John W.; and Usry, J. W.: Data Report of Four Free-DriftingBuoys Tracked by the EOLE Satellite in the Western North AtlanticOcean in the Winter of 19T3. NASA TMX-T2T68. September 19T5•

3. Garrett, L. Ti.; and Pitts, J. I.: A General Transient Neat-TransferComputer Pr*Vam for Thermally Thick Walls. NASA TMX- 2058.August 1970.

A

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C Drawins Sumba

Instrument Housing

Cover Plate, Instrument Housing

Cover Plate, Access Port

Battery i Instrument Deck

Internal Structure, Flotation Disk

Holding Bar

Lifting Lug

Holding Rod

Assembly

Stand-Off, Antenna

Daunting Ring, Antenna

Drag Plate Assembly

Lead Ballast

Daunting Plate, Sensor Plug

Shackel, Drag Plate

Insulator, Antenna

Flotation Blocks

Lifting Bridle

Retai:. —, Lifting Bridle

Flashing Warning Light

Flotation Disk

Support Legs

Bulkhead Sensor Cable ConnectorLocation

Support Legs Location

Antenna Mount Back-up Plate

Warning Flashing Light MouctibgPlate

LX 154,872

LX 154,873

LB 154,874

LX 154,876

LX 154,877

LC 154,878

LC 154.879

LC 154,881

LX 154,882

LB 1540884

LC 154,885

LC 15u,890

LB 154,892

LB 154.893

LB 154,895

LB 154,896

LC 154,897

LC 154,898

LB 154,903

LE 155,096

LX 155,097

LC 155,098

LC 155.110

LC 155,111

LB 155,129

LC 155,130

Table I.- List of buoy components

9

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Figure j. - Photographs of the Insf.rument Housings.

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= 12.23Kg - m2

.^Y = 11.3OKg - m2

izz = 10.10Kg - m2

Y

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Z

MASS = 154.00Kg

Figure 15.- Physical Properties for a Fiberglass Instrument Housing.

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V

Z

Z

I = 13.5 4 Kg - m^xx

I = 13.5 4 rig - m2yy

I = 9.28 Kg - m`zz

mass = 61.363 Kg

Figure 16.- Physical Properties, for the Drogue.

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